Re: [PATCH net-next 1/3] device property: Introduce fwnode_for_each_available_child_node_scoped()

[Javier Carrasco <javier.carrasco.cruz@gmail.com>]

On 11/10/2024 07:39, Sakari Ailus wrote:
> Hi Javier,
> 
> On Tue, Oct 08, 2024 at 06:10:27PM +0200, Javier Carrasco wrote:
>> Introduce the scoped variant of the
>> fwnode_for_each_available_child_node() to automatically decrement the
>> child's refcount when it goes out of scope, removing the need for
>> explicit calls to fwnode_handle_put().
>>
>> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
>> ---
>>  include/linux/property.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/include/linux/property.h b/include/linux/property.h
>> index 61fc20e5f81f..b37508ecf606 100644
>> --- a/include/linux/property.h
>> +++ b/include/linux/property.h
>> @@ -168,6 +168,11 @@ struct fwnode_handle *fwnode_get_next_available_child_node(
>>  	for (child = fwnode_get_next_available_child_node(fwnode, NULL); child;\
>>  	     child = fwnode_get_next_available_child_node(fwnode, child))
>>  
>> +#define fwnode_for_each_available_child_node_scoped(fwnode, child)	       \
>> +	for (struct fwnode_handle *child __free(fwnode_handle) =	       \
>> +		fwnode_get_next_available_child_node(fwnode, NULL); child;     \
>> +	     child = fwnode_get_next_available_child_node(fwnode, child))
>> +
> 
> On OF, the implementation of the .get_next_child_node() fwnode op is:
> 
> static struct fwnode_handle *
> of_fwnode_get_next_child_node(const struct fwnode_handle *fwnode,
>                               struct fwnode_handle *child)
> {
>         return of_fwnode_handle(of_get_next_available_child(to_of_node(fwnode),
>                                                             to_of_node(child)));
> }
> 
> On ACPI we currently have .device_is_available() returning false but that
> probably should be returning true instead (it's been virtually unused
> previously).
> 
> That makes fwnode_get_next_available_child_node() and
> fwnode_get_next_child_node() equivalent on both ACPI and OF. Presumably
> creating unavailable nodes would be useless on swnode, too.
> 
> So my question is: what do we gain by adding all these fwnode_*available()
> helpers?
> 
>>  struct fwnode_handle *device_get_next_child_node(const struct device *dev,
>>  						 struct fwnode_handle *child);
> 

Hi Sakari, thanks for your feedback.

I thought that the difference is not in OF (which either way ends up
calling __of_device_is_available()), but in ACPI.

For fwnode_for_each_child_node(), the ACPI callback is
acpi_get_next_subnode(), and I don't see that the device_is_available()
callback is used in that case.

For fwnode_for_each_available_child_node(),
fwnode_get_next_available_child_node() is used, which checks
fwnode_device_is_available(), which then calls device_is_available().

What's the catch?

Thanks again and best regards,
Javier Carrasco